FIELD OF THE INVENTION, AND RELATED ART AND PRIOR ART STATEMENT
The present invention relates to an optical information recording/reproducing apparatus for performing positioning of a recording/reproducing spot by selection of a pair of photo detecting elements with respect to an optical recording medium such as an optical card or the like.
Generally, an optical-card recording and reproducing apparatus is arranged such that an optical head is arranged in opposed relation to an optical card, and the optical card and the optical head are moved relatively to each other, whereby a light beam from the optical head is irradiated onto an information recording surface of the optical card to scan a light spot formed on the optical card in a track direction in which tracks extend, to thereby perform recording and reproducing of the information.
There are optical cards of the prior art, which include one in which it is assumed to record data along a central line of each track and one in which it is assumed to record respective data along a plurality of lines on both sides of a guide line which is arranged at a center of each of the tracks.
FIG. 1 of the attached drawings shows an arrangement of an optical system and an light-source drive system of the prior-art optical-card recording/reproducing apparatus which has a plurality of light sources. A recording light beam which is generated by a laser diode 31 is brought to a substantially elliptic parallel beam by a collimate lens 32.
The parallel beam is reduced only in a major direction of the ellipse by a shaping prism 33, and is shaped substantially into a circle. A parallel beam diameter is further reduced or throttled such that a spot size of the recording light beam is brought to a predetermined value by a circular iris or stop 34.
The circular parallel beam is so set as to be incident upon a reflecting surface of a polarizing beam splitter 35 substantially at an S-poralization, and almost all of the parallel beam is reflected. A reflected light beam is incident upon a position eccentric from an optical axis of an objective lens 36 only by a. The reflected light beam is converged onto an optical card 37 and is brought to a circular beam spot 50.
Meanwhile, a light source of a reproducing light beam is a laser diode 38 which is arranged separately from the laser diode 31 which generates the recording light beam. The reproducing light beam is brought substantially to an elliptic parallel beam by a collimate lens 39. The parallel beam is shaped substantially into a circle in which only a minor axis direction of the ellipse is enlarged by a shaping prism 40. Subsequently, a parallel beam diameter is further squeezed or throttled by a circular diaphragm or stop 41 such that a spot size of the reproduced light beam is brought to a predetermined value.
The circular parallel beam is brought to a beam in which only one direction (a direction perpendicular to a sheet surface in FIG. 1) within a vertical surface with respect to the optical axis is subject to a refracting action by a plane-concave cylindrical lens 42 so that the circular parallel beam slightly diverges in the direction. The beam which slightly diverges in one direction is so set as to be incident upon the reflecting surface of the polarizing beam splitter 35 substantially at the P-polarization. Accordingly, almost all of the beam is penetrated or transmitted through the reflecting surface of the polarizing beam splitter 35 so that the beam is incident upon a position eccentric from the optical axis of the objective lens 36 only by g, similarly to the recording light beam. The beam is condensed onto the optical card 37. Thus, the beam is brought to a beam spot 51 in the form of a slit elongated in a direction diverged by the cylindrical lens 42.
The optical card 37 is reciprocally moved in a direction indicated by the reference character D. The direction D is in parallel with a track direction along which information tracks 52 extend as shown in FIG. 2.
FIG. 2 shows the circular beam spot 50 due to the recording light beam formed on the recording surface of the optical card 37 and the beam spot 51 in the form of a slit due to the reproducing light beam. The circular beam spot 50 is formed at a center of one of the information tracks 52 on the recording surface. The beam spot 51 in the form of a slit is so formed as to span a plurality of information tracks 52 and guide tracks 53.
As shown in FIG. 1, the recording light beam and the reproducing light beam which are reflected on the optical card 37 passes through the objective lens 36 in an opposite direction and are incident upon a reflecting mirror 43. The recording light beam and the reproducing light beam which are reflected by the reflecting surface of the reflecting mirror 43 are incident upon an imaging lens 44, and are condensed onto a photo detector 45 whose plurality of light receiving elements (photo detecting elements) are arranged on a light receiving surface. An image of the light beam spot on the recording surface of the optical card 37 is formed on the light receiving surface of the photo detector 45.
The laser diode 31 is driven by a laser-diode drive circuit 46, and the laser diode 38 is driven by a laser-diode drive circuit 47. The laser-diode drive circuits 46 and 47 are operated on the basis of a signal from a light-source control circuit 49 within a controller 48 which controls operation of the whole or entire optical-card recording/reproducing apparatus. The laser-diode drive circuit 46 turns on and/or turns off the laser diode 31 with an amount of recording light emission. The laser-diode drive circuit 47 turns on and/or turns off the laser diode 38 with an amount of reproducing light emission.
FIG. 3 shows an arrangement of the photo detector 45. A plurality of light receiving elements are arranged on the light receiving surface of the photo detector 45 so that an image of the light beam spot on the recording surface of the optical card 37 is formed on the light receiving surface.
A pair of focus-detecting-light receiving elements 54 and 55 for the recording light beam, a pair of focus-detecting-light receiving elements 56 and 57 for the reproducing light beam, a pair of track-detecting-light receiving elements 58 and 59 and three (3) pit-detecting-light receiving elements 60, 61 and 62 are arranged on the photo detector 45. A spot image 63 of the recording light beam, a spot image 64 of the reproducing light beam, an image 65 of the pit formed on the information track and images 66 of the guide track are imaged respectively onto proper positions on the light receiving elements.
The focus-detection light receiving elements 54 and 55 of the recording light beam detect a shift in position of the image 63 of the recording light beam spot due to a shift in focus of the recording light beam, as a difference between the light receiving elements 54 and 55, to generate a focus detection signal of the recording light beam.
Meanwhile, the focus detecting light receiving elements 56 and 57 of the reproducing light beam detect, as a difference between the light receiving elements 56 and 57, by a differential amplifier, a shift in position of the image 64 of the reproducing light beam spot due to a shift in focus of the reproducing light beam, to generate a focus detecting signal of the reproducing light beam. The track-detecting-light receiving elements 58 and 59 of the reproducing light beam detect, as a difference between the light receiving elements 58 and 59, a shift in position of the image 66 of the guide track due to a shift in track of the reproducing light beam by a differential amplifier, to generate a track detecting signal of the reproducing light beam.
Moreover, the pit-detection light receiving elements 60, 61 and 62 detect the image 65 of a pit formed on an information track which uniquely corresponds to the pit-detecting-light receiving elements 60, 61 and 62, to generate pit detecting signals of the respective information tracks.
In such optical information recording/reproducing apparatus, wrestling has been made to further increase a storage capacity. Since, however, the prior arrangement is arranged such that a single data train is formed on a single information track, an amount of information capable of being recorded onto the optical card is prescribed or defined by a number of information tracks which can physically be arranged on the optical card. Thus, an increase in the storage capacity cannot so much be expected.
Meanwhile, prior art examples which record a plurality of data trains on a single track are disclosed also in Japanese Patent Laid-Open No. SHO 55-153139 and Japanese Patent Publication No. HEI 3-45456. In Japanese Patent Laid-Open No. SHO 55-153139, rotation of a refracting galvanometer is controlled, and in Japanese Patent Publication No. HEI 3-45456, rotation of a movable mirror is controlled, to perform positioning.
However, in the information recording and reproducing systems of the aforementioned prior art examples, an angularly moving mechanism for angularly moving the mirror and the like, or a semiconductor-laser moving mechanism for moving the semiconductor laser per se is necessary, and a control circuit is also necessary because the spots formed on the recording medium are accurately positioned respectively at a plurality of positions within a single track, and a positioning condition or state must be retained with high accuracy.
For this reason, a mechanism for the optical head and the control circuit are complicated in structure, and weight of the optical head is also heavy. Accordingly, there are a problem that moving speed of the optical head is reduced so that it takes time to access, and a problem that a price of a recording unit which uses the optical head rises.
Meanwhile, FIG. 4 shows the optical card whose structure is capable of recording a plurality of information on a single track.
The optical card has an information recording surface thereof which is formed with a plurality of tracks 403 as shown in FIG. 4. A center of the tracks 403 is provided with guide patterns 402a which extend in a track direction for performing tracking servo control and focus servo control. Each of the guide patterns 402a has both sides thereof which are provided with total eight (8) lines from a data line 1 (L1) to a data line 8 (L8) for recording data.
Furthermore, each of the guide patterns 402a uses together also function of a clock pattern for taking synchronism when writing and reading of the data are performed. The clock pattern is such that portions indicated by white and black are different in reflection level from each other, and a detected signal is binary-coded whereby there can be provided a clock signal for synchronization.
FIG. 5 shows the relationship between an photo detector under a condition positioned on an objective track and the recording medium imaged on the optical detector, to which the focus servo control and the tracking servo control are applied.
A signal of the focus servo and a signal of the tracking servo are generated on the basis of an output from a cell C1 (481) to a cell C4 (484) and a cell D1 (485) to a cell D4 (488) within the optical detector so that the focus control and the tracking control are performed. Upon controlling, the cell C1 (481) to the cell C4 (484) and the cell D1 (485) to the cell D4 (488) are positioned on the guide patterns 402a. Further, since there are provided a plurality of clock cells 489, it is possible to reliably perform detection of the clock from the guide patterns 402a.
Moreover, reading cells 490 arranged sixteen (16) irradiate a data reading beam 480 to the track 403, whereby it is possible to read simultaneously eight (8) line data and eight (8) line data respectively on both sides of the guide pattern 402a, or sixteen (16) line data in sum.
Furthermore, a data writing beam 491 is irradiated only upon data writing, and it is possible to perform writing every one line. At this time, the data writing beam 491 must be positioned on a writing objective line.
A system for recording information onto such optical card in which the plurality of tracks 403 having the guide patterns 402a extending in the track direction and the data lines 1 (L1).about.8 (LB) provided on the both sides of the guide patterns 402a as described above are gathered is disclosed in Japanese Patent Laid-Open No. SHO 63-153727, Japanese Patent Laid-Open No. SHO 62-279523 or the like.
According to Japanese Patent Laid-Open No. SHO 63-153727, a single semiconductor laser is used as a recording light source, and a recording beam due to the semiconductor laser scans in the track widthwise direction by angular movement of a mirror by bimorph or the like, to write information onto a single track of the optical card over a plurality of lines, to thereby raise recording density with respect to the single track.
Further, according to Japanese Patent Laid-Open No. SHO 62-279523, a recording element (semiconductor laser) per se is moved in a track widthwise direction, whereby a recording beam is displaced in the track widthwise direction, to thereby write information over a plurality of lines of a single track.
For this reason, a mechanism of the optical head and a control circuit are complicated in structure as described previously, and weight of the optical head increases. Accordingly, there are problems that moving speed of the optical head decreases so that time is taken for accessing, and a cost of the recording apparatus which uses the optical head increases.